1. Field of the Invention
The present invention relates to a signal processing device, and more particularly, to a signal processing device capable of accurately estimating incoming of a desired signal based on burst frequency or duration time of an input signal.
2. Description of Related Art
In wireless communication devices, it has been required to increase battery life time including stand-by or idle time. In order to meet this requirement, one known method is that a simple signal processing device and main wireless device are prepared and the simple signal processing device detects incoming of radio wave.
For example, Japanese Unexamined Patent Application Publication No. 8-032510 (patent document 1) discloses a circuit that determines presence or absence of a radio signal using a diode detector. As the technique of the patent document 1 does not employ a local signal generating system that consumes large power, it is essentially possible to decrease power consumption. Further, according to the technique of the patent document 1, detecting the radio signal with higher sensitivity is made possible by using an improved diode detector.
Further, the patent document 1 further discloses a circuit which detects that the intensity of the received radio wave exceeds the predetermined intensity, generates a signal having a certain pulse width according to the detection, inputs this signal to an integration circuit, and compares the integrated signal with a predetermined voltage. This technique brings higher likelihood of desired-signal-detection when the desired signal has a certain turn on and off frequency. On the other hand, when the signal is turns on and off with enough lower frequency compared to the desired signal, this signal is classified into an undesired one and is not detected. The similar technique in which an improved diode detector is used includes Japanese Unexamined Patent Application Publication No. 2006-148239 (patent document 2), Japanese Patent No. 2561023 (patent document 3), Japanese Patent No. 2605827 (patent document 4), Japanese Unexamined Patent Application Publication No. 4-291167 (patent document 5), and Japanese Unexamined Patent Application Publication No. 9-162644 (patent document 6).